1. Field of the Invention
The present invention relates to a method of and apparatus for use in orienting an object at a predetermined reference angle with respect to a given plane(s). More particularly, the present invention relates to a process of aligning a chuck relative to equipment by which a substrate supported by the chuck will be processed.
2. Description of the Related Art
Currently, semiconductor memory devices are being developed at a rapid pace due to the widespread use of computers for processing various types of information. To this end, the current art is focused on developing and realizing memory devices having a high degree of integration, response speed, and reliability. Accordingly, highly precise process techniques are required for fabricating today""s semiconductor memory devices.
Semiconductor devices are fabricated by such processes as an ion implantation process, a thin film forming process and a patterning process. Needless to say, all of the conditions under which these fabrication processes are performed must be controlled. If the process conditions are not completely controlled, process errors may be generated. Moreover, a semiconductor substrate is supported by a chuck during semiconductor device fabrication processing, such as during the thin film forming process, pattern forming process, and ion implantation process. Therefore, one of the process conditions usually requiring control is the positioning or aligning of the chuck on which the semiconductor substrate is placed.
The position of the chuck is controlled as follows, using the ion implantation process as an example.
Referring to FIG. 1, a substrate 10 should be tilted relative to an ion beam during the implantation process to prevent a channeling effect from occurring. The channeling effect refers to a situation in which ions injected into the substrate pass through voids in the substrate, i.e., spaces where atoms are not present. Japanese Patent Laid-Open Publication No. 2000-68226 and U.S. Pat. No. 5,406,088 (issued to Brune, et al.) each disclose a method of preventing the channeling effect from occurring during the ion implantation process. More specifically, Japanese Patent Laid-Open Publication No. 2000-68226 discloses a method in which the scanning angle of an ion beam is controlled to prevent the channeling effect. On the other hand, U.S. Pat. No. 5,406,088 discloses a method in which the chuck is manipulated to prevent the channeling effect.
In the latter case, the chuck on which the substrate 10 is placed is preferably tilted at the angle of 7 degrees with reference to the vertical before the ion implantation process begins. The process of tilting the chuck to position the substrate 10 relative to the ion beam will hereinafter be referred to as the process of aligning the chuck.
The process of aligning the chuck includes the steps of first orienting the chuck vertically and then tilting the chuck 7 degrees with respect to the vertical. The step of orienting the chuck vertically is performed by a reference angle providing apparatus shown in FIG. 2.
Referring to FIG. 2, the reference angle providing apparatus 20 is disposed on the bottom surface 17 of the process chamber. The reference angle providing apparatus 20 includes a surface contact portion 200 that makes surface contact with the chuck 15, and a supporting portion 210 for supporting the surface contact portion 200. The supporting portion 210 includes a supporting bar 210a for supporting the surface contact portion 200 and a bottom portion 210b for supporting the supporting bar 210a. The bottom portion 210b is mounted to the bottom surface 17 of the process chamber. The chuck 15 is also mounted to the bottom surface 17 of the chamber.
The surface contact portion 200 of the reference angle providing apparatus 20 is brought into contact with the chuck 15 before the ion implantation process begins. An alignment error is judged to occur at that time if the entire surface of the contact portion 200 does not contact the chuck 15. In that case, X and Y coordinates of the chuck are adjusted such that the chuck 15 contacts the entire surface of the contact portion 200. Preferably, the chuck 15 is oriented at an angle of 0 degrees relative to the X-Y plane (the vertical) and at an angle of 90 degrees relative to the Y-Z plane (the horizontal). Once the chuck 15 and the surface contact portion 200 are in complete surface contact with each other, the chuck 15 is tilted at an angle of 7 relative to the X axis.
However, the reference angle supplying apparatus 20 is subject to the following problems. First, the apparatus 20 itself is moved manually to place the surface contact portion 200 in contact with the chuck 15. Therefore, the apparatus is shaken during this operation, which shaking can cause an alignment error to occur. Also, alignment errors are produced because the bottom portion 210b of the reference angle supplying apparatus 20 is often does not lie precisely flat on the bottom surface 17 of the chamber. Still further, the state of contact between the chuck 15 and the surface contact portion 200 is judged by an operator, whereby the alignment process is prone to human error. Furthermore, the precision or calibration of the reference angle supplying apparatus 20 degrades over time. However, the apparatus 20 has no means by which its own misalignment can be detected. Therefore, the apparatus 20 may be operated continuously while being out of self-alignment. As a result, the chuck 15 is oriented improperly by the apparatus 20.
For the reasons described above, process errors frequently occur when the chuck is aligned using the conventional reference angle providing apparatus. Accordingly, these errors translate so much into the process of fabricating the semiconductor device that the productivity of the fabricating process suffers.
An object of the present invention is to obviate the above-described problems of the prior art. Accordingly, an object of the present invention is to provide a method and apparatus by which an object to be aligned may first be oriented precisely at a desired reference angle.
To achieve this object, the present invention provides an apparatus for providing an object with a reference angle, which apparatus comprises a main body and a pin gauge for making point contact with the surface of the object.
The pin gauge has at least two projections which project in the direction of a Z axis away from an end surface of the body. Two or more of the projections are located on X and Y axes, respectively, orthogonal to one another and to the Z axis and spaced from the origin of the coordinate system defined by the X, Y and Z axes.
In addition, a mechanical drive member(s) is/are used to bring the pin gauge into initial contact with the object to be aligned. In particular, a horizontal support having a horizontal guide engaged with the main body, and a horizontal drive member are used to move the body horizontally in the direction of the Z axis (longitudinal direction of the projections of the pin gauge) to bring the pin gauge into initial point contact with the object. A vertical support having a vertical guide, and a vertical drive may also be provided to bring the pin gauge up or down to the level of the object to be aligned.
The vertical support may include a bottom member on which the horizontal support is disposed, and a vertical member on which the vertical guide is disposed. The vertical guide is engaged with at least the horizontal support.
Each mechanical drive member preferably comprises a fixed nut and a drive screw connected to the main body and threaded with the fixed nut. Thus, the drive screw and the body of the apparatus connected thereto will be moved linearly when the drive screw is rotated relative to the fixed nut. An actuating member, such as a knob, allows the drive screw to be rotated.
Preferably, the projections comprise proximity sensors for sensing the distances between the ends of the projections and the object. Also, a display is used for displaying the measurements made by the proximity sensors. Therefore, the position of the object relative to the pin gauge providing the reference angle is not judged by the operator but by the sensors. And, the results are displayed to the operator. That is, the relative position of the object is determined objectively. As a result, errors in the process of aligning the object can be minimized.
Furthermore, a reference angle calibration unit can be used to check the accuracy of the reference angle providing apparatus. The calibration unit has a reference surface against which the pin gauge can be pressed to check the state of point contact. In this way, if the pin gauge is determined to have become inaccurate due to its continuous use over a long period of time, the pin gauge can be repaired. Accordingly, the reliability of the apparatus is ensured.
For instance, the reliability in of the apparatus in facilitating the aligning of a chuck of semiconductor fabricating equipment is ensured. In this case, the reference angle providing apparatus is placed on the bottom surface of a process chamber in which the chuck is disposed. The pin gauge is moved mechanically towards the chuck until the pin gauge contacts the surface of the chuck. Accordingly, the gauge is not shaken as it contacts the chuck, whereby the maintains a high degree of accuracy.
Once the pin gauge contacts the surface of the chuck, the state of point contact between the end of each of the projections of the pin gauge and the surface of said chuck is checked, i.e., the distances between the projections of the pin gauge and the surface of the chuck is sensed by the proximity sensors. The chuck is then pivoted, if necessary, to place the surface of the chuck in point contact with the ends of all of the projections of the pin gauge. Hence, the chuck is oriented at the reference angle. Finally, the chuck is tilted a predetermined amount from the reference angle. In the case of an ion implanter, the chuck is tilted 7 degrees to prevent the channeling effect from occurring during the implantation process.